4. Alternate additions of baking powder and milk, beating well between each addition. Put half this batter into the melted chocolate and whisk to combine. Put the other half into a large bowl.

5. Add 100 grams of flour to the bowl with the chocolate and stir to combine. Add the other 100 grams of flour to the other bowl with the non-chocolate batter and stir to combine.

6. Whisk the egg whites and sugar until soft peaks form. Fold half into the bowl with the chocolate batter, and half into the other bowl.

7. Put the non-chocolate batter on the bottom of the pan, then put the chocolate batter on top. If you are feeling brave, cut with a knife to create a marbled effect (or just leave it as two distinct layers).

8. Bake for 60 minutes, covering with foil halfway through to prevent the top from burning if necessary. (We have a convention oven and it was very necessary to cover the cake with foil.)

9. Turn out cake on wire rack to cool. Dust with confectioners sugar to serve.